The long term goal of this research is to provide biomedical researchers with a selection of photoreactive functionalities that can be incorporated into bioactive molecules. These groups will permit the cross-linking of macromolecules and small molecules so as to identify sites of interaction and the preparation of bioactive molecules in specific locations. The groups to be developed are designed to be superior to currently used groups regarding their efficiency of reaction, quantum yield, wavelength of activation, by-products, and ease of incorporation into biomolecules. The project also aims to develop methods whereby such groups can be used to localize different biological components for assembly into large ensembles with special functions or as model systems. The specific aims of this project are to develop new photoremovable silyl groups, nitrobenzyl groups, and phenylglyoxyl groups. These photoremovable groups will be used in "caging" (protecting from reaction by a photoremovable group) serine and enols. Caging is useful in locating an inactive effector molecule and rapidly activating it to observe its biological effects or chemical reactivity. Photoremovable groups will be used in the synthesis of DNA sequences at specific locations on a surface. Photoactivatable surfaces that can bind cells in irradiated zones will also be developed. The key to the methods to be developed in the project is the ability to spatially direct light and to detect binding by fluorescence. The ability to synthesize DNA in defined locations will permit a number of new applications of nucleic acid hybridization to be developed, including diagnostics, clone mapping, and DNA sequencing.